In the past, a multiplicity of proposals have been made as to how it is possible in the case of vehicles that are used as robots for inspection or repair in pipe systems or other cavities to employ simple passive mechanisms so as to ensure that the vehicles can automatically negotiate corners or more generally concavely constructed obstacles. One of these proposals, which can be designated as wheel inside the wheel, is known from the publication JP7246931A. The principle of this known solution can be explained with the aid of FIG. 1: the known drive unit 36 comprises as essential elements a ring-like outer wheel 37 on whose inner peripheral surface a magnetic wheel 38 of very much smaller outside diameter can roll along. The rolling operation is configured in this case by a toothing (not illustrated) such that it proceeds without slippage. The magnetic wheel 38 is driven by a device that is not illustrated in the figure. As the vehicle moves, the outer wheel 37 rolls along on the underlying surface on which the vehicle is moving.
When, as illustrated in FIG. 1, an obstacle in the form of an edge or step 39 is located in the movement path of the vehicle, which is fitted with the drive unit 36, the rolling movement of the outer wheel 37 is stopped—as shown in FIG. 1b. The stationary outer wheel 37 forms in the region of the edge 39 a type of curved ramp on which the driven magnetic wheel 38 can roll upward (FIG. 1c). In this way, the magnetic wheel 38 increasingly leaves the region of magnetic attraction lying ahead of the edge 39 and dives into the region of magnetic attraction lying behind the edge 39. This has the effect that the outer wheel 37 can roll further away over the edge 39. The obstacle is easily negotiated in this way by the wheel inside the wheel mechanics.
However, this known solution has various disadvantages: as illustratively seen in FIG. 1a, there exist for the magnetic flux density between the magnetic wheel 38 and the underlying surface two linear contacts LC1 and LC2 that substantially weaken magnetic forces during the normal rolling movement.
In the case of the configuration specified in the publication JP7246931A, a pair of magnetic wheels 38 lying far apart from one another are supplied with magnetic force by a long magnet arranged therebetween. On the one hand, this reduces the magnetic force on the magnetic wheel 38. On the other hand, the rigid coupling of the two magnetic wheels 38 by the magnet arranged therebetween prevents the possibility of being able to steer the vehicle by differences in the rotational speed of the two magnetic wheels 38.
If the magnetic wheels of a pair were to be moved more closely together in order to form a compact drive wheel with a higher magnetic force, the outer wheel would need to be designed to be nonmagnetic in the region between the two magnetic wheels in order to prevent a magnetic short circuit between the two magnetic wheels. However, this is very demanding in terms of production engineering, particularly when the wheels involved must be small.